Editing Mariner 1 (section)

==Background==

[[File:Mariner 2 trajectory.jpg|thumb|Mariner II [[trajectory]] projected on the [[ecliptic plane]].]]

With the advent of the [[Cold War]], the two then-[[superpower]]s, the [[United States of America|United States]] and the [[Soviet Union]], both initiated ambitious space programs with the intent of demonstrating military, technological, and political dominance.<ref name=history/> The Soviets launched the [[Sputnik 1]], the first Earth orbiting satellite, on October 4, 1957. The Americans followed suit with [[Explorer 1]] on February 1, 1958, by which point the Soviets had already launched the first orbiting animal, [[Laika]] in [[Sputnik 2]]. Earth's orbit having been reached, focus turned to being the first to the Moon. The [[Pioneer program]] of satellites consisted of three unsuccessful lunar attempts in 1958. In early 1959, the Soviet [[Luna 1]] was the first probe to fly by the Moon, followed by [[Luna 2]], the first artificial object to impact the Moon.<ref name=encyclopedia/>

With the Moon achieved, the superpowers turned their eyes to the planets. As the closest planet to Earth, [[Venus]] presented an appealing interplanetary spaceflight target.<ref name=treasury/>{{rp|172}} Every 19 months, Venus and the Earth reach relative positions in their orbits around the Sun such that a minimum of fuel is required to travel from one planet to the other via a [[Hohmann Transfer Orbit]]. These opportunities mark the best time to launch exploratory spacecraft, requiring the least fuel to make the trip.<ref name=Hohnmann/>

The first such opportunity of the Space Race occurred in late 1957, before either superpower had the technology to take advantage of it. The second opportunity, around June 1959, lay just within the edge of technological feasibility, and [[United States Air Force|U.S. Air Force]] contractor [[TRW Inc.|Space Technology Laboratory]] (STL) intended to take advantage of it. A plan drafted January 1959 involved two spacecraft evolved from the first Pioneer probes, one to be launched via [[Thor-Able]] rocket, the other via the yet-untested [[Atlas-Able]].<ref name=DevPlan/> STL was unable to complete the probes before June,<ref name=Able34/> and the [[launch window]] was missed. The Thor-Able probe was repurposed as the deep space explorer ''[[Pioneer 5]]'', which was launched March 11, 1960, and designed to maintain communications with Earth up to a distance of {{cvt|20000000|mi}} as it traveled toward the orbit of Venus.<ref name=P5/> (The Atlas Able probe concept was repurposed as the unsuccessful [[Pioneer P-1|Pioneer Atlas]] Moon probes.)<ref name=ableseries/> No American missions were sent during the early 1961 opportunity. The Soviet Union launched [[Venera 1]] on February 12, 1961, and on May 19–20 became the first probe to fly by Venus; however, it had stopped [[transmitter|transmitting]] on February 26.<ref name=NSSDC-2/>

For the summer 1962 launch opportunity, NASA contracted [[Jet Propulsion Laboratory]] (JPL) in July 1960 <ref name=treasury/>{{rp|172}} to develop "Mariner A", a {{cvt|1250|lb}} spacecraft to be launched using the yet undeveloped [[Atlas-Centaur]]. By August 1961, it had become clear that the [[Centaur (rocket stage)|Centaur]] would not be ready in time. JPL proposed to NASA that the mission might be accomplished with a lighter spacecraft using the less powerful but operational [[Atlas-Agena]]. A hybrid of Mariner A and JPL's Block 1 [[Ranger program|Ranger]] lunar explorer, already under development, was suggested. NASA accepted the proposal, and JPL began an 11-month crash program to develop "Mariner R" (so named because it was a Ranger derivative). Mariner 1 was the first Mariner R to be launched.<ref name=report/>